Modulated continuous-wave operation



Dec. 1, 1942. M D N 2,303,484

MODULATED CONTINUOUS-WAVE OPERATION Filed Aug. 13, 1940 I WITNESSES:INVENTOR Z,MW (W/ J m; (/5811.

Patented Dec. 1, 1942 MODULATED CON TINUOUS-WAVE OPERATION Carl J.Madsen, Woodlawn, Md., assignor to Westinghouse Electric & ManufacturingCompany,

Ealsita Pittsburgh, Pa., a corporation of Pennsyl- Application August13, 1940, Serial No. 352,348 4 Claims. (01. 179-1715) My inventionrelates to continuous-wave generating systems often employed forcommunication and direction-finding purposes and, in particular, relatesto a system which can be employed at will either for generatingcontinuous waves of substantially constant amplitude or for producingcontinuous waves which are modulated in accordance with the frequency ofa local generating source.

One object of my invention is to provide a system which may be changedfrom modulated continuous-wave generation to constant amplitudecontinuous-wave generation with a minimum number of alterations in thecircuit connections.

Another object of my invention is to provide a system which can bealtered from modulated continuous-wave to straight continuous-waveoperation without switching operations in the grid circuits of the audiooscillator and which will operate without such circuit changes whilestill maintaining substantially the same output wave form in each of theabove-mentioned modes of operation.

Other objects of my invention may become apparent upon reading thefollowing specification taken in connection with the single figure ofdrawing, which is a circuit diagram of an interconnected radio-frequencyamplifier and audiofrequency oscillator adapted to form a portion of acontinuous-wave transmitting system and embodying the principles of myinvention.

In the drawing, a radio-frequency amplifier I, which may be of thepentode type, has its anode 2 and cathode 3 supplied with voltage from adirect-current source 4 of the variable potentlometer type well known inthe radio art. The plate circuit of the tube I is provided with avariable capacitor 5 and an inductor 6 for coupling it to a load or toother amplifiers in a manner conventional in the radio art. A capacitor8 is provided which has one terminal grounded and thereby connected tothe grounded negative end of the voltage source 4 to bypassradio-frequency currents in a manner conventional in the art. The tube Imay likewise be provided with a screen grid 9 grounded through acapacitor II and connected through an inductor I2 to an appropriatepoint of voltage on the source 4. The tube I is likewise provided with acontrol grid l3 which is connected through an input source I4 to aproper bias potential point on the direct-current source 4 in a mannerconventional in the radio When any desired carrier wave, which may, whendesired, vary in accordance withsignals to be transmitted, is impressedupon the input element I4, the output circuit connected 0 the plate 2will transmit an amplified replica of the voltage impressed on the inputelement I4 as a result of th connections so far described, and isadapted to operate for continuous-wave transmission.

In order to provide for modulated continuouswave transmission whendesired, a second tube 2|, which may have a cathode, an anode and acontrol grid, is arranged to derive current from the voltage source 4througha winding 22. The control electrode of the tube 2| is connectedto a suitable bias point on the voltage source 4 through a resistor 23and an anti-resonant circuit comprising a capacitor 24 connected acrossthe terminals of a winding 25 which is in inductive relation to thewinding 22. A capacitor 26 may be provided to connect the cathode end ofthe winding 25 to ground, and a capacitor 21 be provided to connect thepositive end of the winding 22 to ground to form alternating-currentbypasses in accordance with practice well known in the radio art. Byproper poling and adjustment of the windings 22 and 25, the tube 2| may,in a manner well known in the radio art, be made to generateaudio-frequency oscillations of the frequency at which it is desired tomodulate the continuous-wave output of tube I. To impress theaudio-frequency oscillations of the tube 2| upon the radio-frequencyamplifier I, the grid of tube 2| is connected to the suppressor grid I5of the tube I When the tube 2| is rendered operative by raising itscathode to an electron-emitting temperature, the tube 2| will generateoscillations of the desired frequency for modulation of the output ofradio-frequency amplifier and impress them upon the output thereof. Thesystem is thus arranged for modulated continuous-wave operation. Whennow it is desired to operate the system as a straight continuous-wavedevice, a switch 28 in the cathode circuit of the tube 2| may be opened,thereby deenergizing it; when this is done, it may be found that theradio-frequency amplifier continues to operat with a good output and anundistorted wave form.

With a source of 2000 volts impressed upon the anode circuit ofradio-frequency amplifier I,

a source of 1000 volts impressed upon the plate art. The tube i islikewise provided with a suppressor grid I5 which is connected to groundin a conventional manner through a capacitor I8.

of the oscillator tube 2|, and from 300 volts to 600 volts impressedupon the grid 9 of radiofrequency amplifier I, I have found that amaximum output is obtained from the radio-frequency amplifier l duringcontinuous-wave operation if the control grid of the tube 2| is biasedto a 3 positive potential or from .zero to 60 volts.

voltage on the grid I! in radio-frequency amplifier I, may be varied toobtain the most desirable wave form and amplitude of the output currentfrom the circuit of plate 2 or the radioirequency amplifier.

While the radio-frequency amplifier tube I has been described as havinga screen grid 9, it will be recognized that a tetrode in which thisscreen grid is omitted'may be usefully employed for certain conditions.Likewise, it will be recognized by those skilled in the art that, whilethe audioirequency oscillator 2| has been described as a triode, atetrode or a pentode arranged for audioirequency oscillation inaccordance with connections well known in the radio art may replace sucha triode.

While in accordance with the patent statutes I have described a specificembodiment of the principles 01 my invention, it will be recognized thatthey are capable of broader application in ways which will be evident tothose skilled in the art.

I claim as my invention:

1. In a carrier-wave modulation system, a radio-frequency amplifier tubehaving an anode, a cathode and at least two control electrodes, an inputcircuit adapted to impress a carrier wave upon one of said controlelectrodes, an output circuit connected to said anode, an oscillationgenerator tube comprising a cathode, an anode and at least one controlelectrode, a bias resistor connected between the last-mentioned cathodeand the last-mentioned control electrode, a connection conductive todirect current from a second control electrode of the first-mentionedtube to a point on the circuit of said resistor, and means forselectively rendering said generator operative and inoperative whilesaid amplifier is maintained operative.

2. In a carrier-wave modulation system, a radio-frequency amplifier tubehaving an'anode, a cathode and at least two control electrodes,

an input circuit adapted to impress a carrier wave upon one of saidcontrol electrodes, an output circuit connected to said anode, anoscillation generator tube comprising a cathode, an anode and at leastone control electrode, a bias resistor connected in a circuit betweenthe last-mentlonedcathode and an anti-resonant circuit connected to thelast-mentioned control electrode, and a connection from a second controlelectrode of the first-mentioned tube to a point on the circuitincluding said bias resistor remote from said last-mentioned cathode.

3. In a system for transmitting carrier waves, an amplifier tube havingan anode, a cathode and at least two control impressing a carrier waveon one of said control electrodes, a vacuum-tube oscillation generatorcomprising an anode, a cathode and a control electrode, means forcoupling the circuit otthe lastmentioned control electrode and thelast-mentioned anode to cause said oscillator to generate amodulating-frequency current, a connecting channel between thefirst-mentioned cathode and the second-mentioned cathode, a biasresistor between the second-mentioned cathode and its associated controlelectrode, and a connection from a second control electrode in thefirst-mentioned tube on the circuit of said resistor, and means forselectively rendering said generator operative and inoperative whilesaid amplifier is maintained operative.

4. In a system for transmitting carrier waves. anamplifier tube havingan anode, a cathode and at least two control electrodes, means for Iimpressing a carrier wave on one of said control electrodes, avacuum-tube oscillation generator comprising an anode, a cathode and acontrol electrode, means for coupling the circuit of the last-mentionedcontrol electrode and the lastmentioned anode to cause said oscillatorto generate a modulating-frequency current, a connecting channel betweenthe first-mentioned cathode and the second-mentioned cathode, a biasresistor provided with bypass capacitance between the second-mentionedcathode and its associated control electrode, and a connection from asecond control electrode in the first-mentioned tube to a point on thecircuit of said resistor, and means for selectively rendering saidgenerator operative and inoperative while said amplifier is maintainedoperative.

ARL J. MADSEN.

electrodes, means for

